“Orbital variations (eccentricity) remain the most thoroughly examined mechanism relative to climatic change on time scales of tens of thousands of years and are by far the clearest case of a direct effect of changing insolation (the amount of solar radiation) on the lower atmosphere of the Earth” From National Research Council of United States National Academy of Sciences 1982)

ECCENTRICITY measures how much the shape of Earth’s orbit departs from a perfect circle. These variations affect the distance between Earth and Sun.

OBLIQUITY The angle Earth’s axis of rotation is tilted as it travels around the Sun is known as obliquity. Obliquity is why Earth has seasons. Over the last million years, it has varied between 22.1 and 24.5 degrees with respect to Earth’s orbital plane.

PRECESSION of the equinoxes, motion of the equinoxes along the ecliptic (the plane of Earth’s orbit) caused by the cyclic precession of Earth’s axis

For over 50 years, Milankovitch’s theory was largely ignored. Then, in 1976, a study published in the journal Science examined deep-sea sediment cores and found that Milankovitch’s theory did in fact correspond to periods of climate change. Specifically, the authors were able to extract the record of temperature change going back 450,000 years and found that major variations in climate were closely associated with changes in the tgeometry (eccentricity, obliquity, and Precession) of Earth’s orbit. Indeed, ice ages had occurred when the Earth was going through different stages of orbital variation. “A model of future climate based on the observed orbital-climate relationships, but ignoring anthropogenic effects, predicts that the long-term trend over the next 7,000 years is toward extensive Northern Hemisphere glaciation” J. D. Hays,  John Imbrie  and N. J. Shackleton.